This invention relates generally to a low cost system to utilize waste heat produced in a process.
Recovery of waste heat from combustion sources is an important way to achieve energy conservation that is widely practiced in industry. The waste heat can be used to provide useful heat to a process or to generate power using a heat engine. Some examples are regenerative heating in a glass furnace, generation of hot water for heating from an engine exhaust and generation of steam for power generation from the exhaust of a large gas turbine. However, some sources of waste heat have characteristics that result in excessively high costs to generate useful thermal or power output. These include low temperature, small size, remote location and/or corrosive products. Some examples include landfill gas flares and engine generators which are remote from any useful thermal loads.
Accordingly, there is need for a low cost, efficient method to recovery the waste heat from sources which have not been widely used because of the heretofore uneconomic characteristics.
It is a major object of the invention to provide apparatus and methods meeting the above need. Basically, the apparatus of the invention includes a waste heat recovery system comprising:
a) ducting to which hot gas is communicated,
b) means to supply lower temperature diluent gas to the ducting, to mix with the hot gas, and produce a reduced temperature mixed gas stream,
c) a vaporizer in communication with the ducting, to receive the gas stream and to transfer heat from the stream to a working fluid in the vaporizer to vaporize that fluid,
d) and a blower operating to displace the gas stream through the vaporizer.
Typically, the blower is of induction type, having an inlet to which the mixed gas stream is supplied after passage through the vaporizer, i.e. the system operates by suction induced stream flow through the vaporizer, such suction also being utilized to induce mixing of the hot gas and cooler gas, in the ducting upstream of the vaporizer. A highly efficient system is thereby achieved.
Another object of the invention is to provide a through opening or openings in a side wall of the hot gas ducting, to pass the lower temperature diluent gas into the ducting in response to suction creation by the blower and communicated to said ducting via the vaporizer. A refractory sleeve or sleeves may be provided in the side wall opening or openings, to block loss of heat to the exterior of the ducting via the side opening or openings.
The system enables use of vaporized working fluid by means to create electric power; and a diverter valve may be advantageously supplied in series with the ducting to
i) divert said stream to atmosphere when the the above reference electric power producing means is not operating to produce electric power;
ii) pass said stream to the vaporizer when said means is operating to produce electric power.